Building Tesla coils need help calculating bleed resistors.

johnboyman

Joined Jun 1, 2019
39
Hey guys I am just about to run my 15,000 volt tesla coil. The total capacitance i need for this coil is 0.025 uF. I bought 13, .33 uF caps. I need bleed resistors now. I calculated that i need .6 mega ohm resistors so far. 15,000/.025 = 600,000. = .6 Megaohm resistors. I don't know how to calculate the wattage for each resistor. I look around on the internet and i see many different answers but no straight answer so before I go out shopping I really wanted to ask some pros. When i finish i Want to show of my amazing coil. Thanks for the help if any, bye.

Joined Mar 10, 2018
4,057

johnboyman

Joined Jun 1, 2019
39
Yes that post kind of makes sense but kinda is why i am lost. I see people using 1/2 watt resistors for these powerful setups. I don't know how this adds up. So is the wattage per resistor 1200*.025 uF. That would be 30. 30 watts is not 1- 1/2 watt. I have gone over this before many times in my head and can't see how people are using such a small resistor? Thanks

Joined Mar 10, 2018
4,057
To calculate wattage you need to know either current thru resistor
or the Vdrop across it when in operation. We sorta know the latter
so P = (E x E) / R where E = 1200V and R you know.
So I get 2.4W. So either get that wattage or raise the R value. Surfing
web I see some folks using as high as 10 Meg Ohms. Regards, Dana.

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johnboyman

Joined Jun 1, 2019
39
Thanks alot. What is the reason for using the p = e*e/r. Where is that formula on the chart you showed? Thanks.

Joined Mar 10, 2018
4,057
That is the same as V squared / R on the chart. V & E are voltage, I should have
used V to be consistent, my error.

Regards, Dana.

johnboyman

Joined Jun 1, 2019
39
Ok thanks alot. This is making sense now. I need to do some more research on this chart thanks.

rsjsouza

Joined Apr 21, 2014
344
Another way to make sense is if you have memorized both Ohm's and Joule's laws:
V = R × I ⇒ I = V / R
P = V × I

Combining the two above: P = V × (V / R)

Other combinations are easy to be done:
P = (R × I) × I

johnboyman

Joined Jun 1, 2019
39
how do i know when to use thoughs ones though, why in this particular case do you combine forumlas?

johnboyman

Joined Jun 1, 2019
39
Using I * v for watts is the only forumla i understand, why are the others there and when do you use them.

rsjsouza

Joined Apr 21, 2014
344
Using I * v for watts is the only forumla i understand, why are the others there and when do you use them.
P = I × V is a variant of the Joule's law, which was originally stated as P = R × I^2

V = R × I is the Ohm's law, another very important equation

You may benefit from reading the following article:
https://en.wikipedia.org/wiki/Joule_heating#Formulas

MisterBill2

Joined Jan 23, 2018
10,587
I have no recollection of ever seeing a bleeder resistor as part of a Tesla coil system. So I am really wondering about that. What part of the circuit gets a bleeder across the caps? Or are they actually equalizer resistors to keep a similar voltage across each cap in a series string?

Alec_t

Joined Sep 17, 2013
12,479
15,000/.025 = 600,000
How did you arrive at that ".025" figure? It seems entirely arbitrary.

KeepItSimpleStupid

Joined Mar 4, 2014
5,090
What a mess.

Bleeder resistors basically discharge the capacitors in a reasonable amount of time. A figure of merti is 5*RC where the circuit would be about 98-99% discharged.

You pick a t Say 120s for 5*RCl t=5*R*C
You know C
Pick an R that doesn't break your power supply. Say 5-10% of the total current capacity. Using R=V/(1*0.01)

So, R (ohms) * C (Farads) = seconds. RC is known as the time constant.

Find power disipated by resistor. Make wattage larger.

See: http://www3.ncc.edu/Faculty/ENS/schoenf/ELT115/UCC.html

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MisterBill2

Joined Jan 23, 2018
10,587
Tesla coil systems do not need bleeder resistors!

Ylli

Joined Nov 13, 2015
1,054
The total capacitance i need for this coil is 0.025 uF. I bought 13, .33 uF caps. I need bleed resistors now.
These would not be 'bleed' resistor, but rather equalizing resistor. 0.33uF/13 = 0.025uF.

Papabravo

Joined Feb 24, 2006
17,617
Sure am glad you guys all seem to know WTF you are doing. We don't want to be giving out Darwin Awards this summer.